One of our main goals is to provide our customers with a great cache hit rate, with an average of over 95%. If your pull zone is displaying a low cache hit rate, it means that the requests are not being cached on our servers and we always fetching them from your origin URL first. This not only stresses your server but also provides. If you are seeing anything below 70%, it is is very likely an indicator of a performance problem caused by an incorrect configuration, but luckily, there are a few easy ways to test and fix this.
Look at the 'Cache-Control' header of your files
The first thing that we recommend you to do is have a look at your Cache-Control headers on your static files. Our servers will strictly follow this header in order to determine if the files should be cached, and for how long.
Some of the indicators of a Cache-Control header error:
- The Cache-Control is missing.
- The value is set to no-cache
- The value is missing the max-age directive
- The value contains a very low max-age value
You can easily check this using the curl command that would look as follows:
curl -I http://static.examplesite.net/css/style.css
HTTP/1.1 200 OK
Date: Fri, 03 Mar 2017 16:09:24 GMT
If you found any of the problems above, it's is likely the reason why your hit rate is so low. Luckily, there is a relatively easy solution for this.
Are you using dynamic query strings when linking to your static files?
This is also a very easy and big indicator why things are not being cached. We look at each URL as a unique entity, so if the query string changes, it won't get loaded from cache as our servers will assume this might be a different URL. For example, if you are linking to files with query strings like this /style.css?v=5ga356q and the next time like this /style.css?v=qwf34f we will treat these two URLs as two different files.
This can be used with good advantages, for example, when making sure that the user has the latest version of the file, but when used incorrectly, it might happen that the strings are changing, while representing the same content.
Luckily, we provide an easy way to solve this.
In your dashboard, simply go to Pull Zones -> Manage Existing -> Pull Zone Details and in the CACHE SETTINGS tab, you will see a section called Ignore URL query strings. All you have to do now is enable this feature. Our system will now automatically treat /style.css?v=qwf34f and /style.css?v=5ga356q as two identical URLs and will always serve the same cache file for both, instantly improving your cache hit rate.
Is your Pull Zone new or did you just do a cache purge?
When you first create your Pull Zone, the cache hit rate slowly builds up, so if you just created it, you might want to simply wait for a day and you should be seeing an increase in the cache hit rate as hours go by. The same goes if your Pull Zone was just purged. If you purge cache, we recycle everything already stored on our servers and start loading your resources fresh from the server.
If any of the two is true, you might simply wait a bit to see if the cache hit rate goes up and if not, have a look at point 1 and 2 of this article.